ASoC: msm8939: fix no audio after SSR

In case of Slimbus based external codec in 8939,
machine driver need to provide event callback
to codec driver. Also machine driver registers
to subsys notifier to get events for modem restart.

Change-Id: I9e73568e820ae6da7c92c0476b7a9ffd78bf5171
Signed-off-by: Laxminath Kasam <lkasam@codeaurora.org>